WASHINGTON — Stopping the Ebola virus from spreading in Africa is the best way to protect everyone worldwide, U.S. Centers for Disease Control chief Tom Frieden told House members at a hearing Thursday.

"We can stop Ebola: We know how to do it," he said. "We have to stop it at the source in Africa. That's the only way to get control."

The hearing — unusual because Congress is on August recess — comes on the heels of a highest-level alert Thursday morning in response to the outbreak. The CDC has moved to a "Level 1" response, which means the government has increased staff and resources to address the situation. Frieden said on Twitter Wednesday that the outbreak has the potential to "affect many lives."

About 50 people from the CDC have been sent to West Africa to help, and the World Bank has pledged $200 million.

But Ken Isaacs, vice president of program and government relations at Samaritan's Purse, said containment of the disease and international response has been "a failure," and that he and members of his organization had been warning of the impending outbreaks since April.

"That the world would allow two relief agencies to shoulder this burden along with the overwhelmed Ministries of Health in these countries testifies to the lack of serious attention the epidemic was given," Isaacs said. No one paid attention until two Americans on the Samaritan's Purse team became infected, he said.

He said epidemiologists expect the disease to spread, and then to go quiet for three weeks, and then to reemerge even worse. "I think we are going to see the death toll in numbers we cannot imagine," Isaacs said. "In the developing world, it has the potential to destabilize entire countries while creating widespread and even regional insecurity."

The international response, he said, needs to increase substantially.

Missionary and doctor Frank Glover said Liberia only has 50 doctors in clinical care because 95% of doctors from other countries left, and nurses have not been paid in six months. Bodies are buried in mass shallow graves near water supplies after laying in the streets for days because funeral workers have not been paid. And whole families have gotten sick because there's no place for people to go.

He called the health system "inherently weak," and said that thousands of people in Liberia could die if immediate changes are not made.

But Frieden reiterated that people who don't have symptoms of the disease cannot spread it, and that it has to be spread through close contact with a sick person. In West Africa, family members often tend to the bodies of dead relatives in preparation for funerals, leading them to also become sick.

"Those are the drivers of Ebola in Africa," he said. "We, with our partners, have been able to stop every (prior) outbreak of Ebola to date."

But he said it would not be easy, and that just one infected patient who is not quarantined could hurt the effort.

"It is certainly possible that we could have ill people in the U.S.," Frieden said. "But we are confident there will not be a large Ebola outbreak in the U.S."

People with fevers who have been exposed to the virus should have a blood test to see if they have been infected, and then interviewed to identify people they have been in contact with, he said.

"The current outbreak is a crisis," said Frieden. "It is unprecedented."

Ariel Pablos-Méndez, assistant administrator for the bureau for global health at the U.S. Agency for International Development, said a disaster assistance response team has been deployed.

"We are confident that we can stop the epidemic," he said. "It will not be easy, and it may take several months."

Ambassador Bisa Williams, deputy assistant secretary at the Bureau of African Affairs at the U.S. Department of State, said

the outbreak has already affected international security because a peace-keeping force from Sierra Leone has not deployed to Somalia as planned because of fears of spreading the disease.

Rep. Christopher Smith, R-N.J., chair of the House Subcommittee on Africa, Global Health, Global Human Rights and International Organizations, said, "Even when there was an outbreak, such as in Uganda, international cooperation was able to prevent a broader spread of the disease."

There have been more than 1,700 cases of Ebola, and nearly 1,000 deaths, in the current outbreak in Guinea, Liberia, Nigeria and Sierra Leone. Ebola spreads through bodily fluids, and causes vomiting and diarrhea, as well as internal bleeding in some patients.

Smith asked that Congress reconsider the budget for infectious disease, which has been dropping over the past few years.

Rep. Karen Bass, D-Calif., said that because there has not been an outbreak in West Africa before, local officials were unaware of how to deal with it.

"We do know how to stop the spread of this disease," Bass said, adding that West Africa needs help with training, as well as food and water in the affected areas. "It is obviously in our interest and the interest of the world to assist in this crisis."